Why is the shoulder moving when I move the left forearm bone?
Select the mesh, activate the two little buttons on the armature modifier so that it shows its effetc also in edit mode, then move the forearm in pose mode. Back to the mesh in edit mode select one of the vertices that is movin weird: in the "N" properties panel you will see that they have some weight from forearm bone (maybe 0.000001) and expecially from the f_pinky03.L bone: thoose weights are causing the unwanted deformation. So select all the weird vertices and remove all weights to have everything fine.

Remember that even a very tiny weight, if it's not "balanced" by another bigger one, will cause a big movement, because Blender does an automatic normalisation between all assigned weights.